The scope of the present invention is that of initiation devices for a pyrotechnic system, and more particularly, initiation devices which enable the initiation of the deconfinement of an envelope containing a pyrotechnic charge, such as a propelling charge or an explosive charge.
The function of such deconfinement devices is to ensure the opening of the envelope which contains the pyrotechnic charge when the envelope temperature rises above a certain level.
Such a deconfinement avoids the detonation of the charge resulting from an increase in the envelope temperature.
In fact, when a munition is subjected to a high temperature, for example during the outbreak of a fire in the storage facility, the pyrotechnic charge which is contained within the envelope decomposes.
This decomposition produces gases which in turn cause the pressure inside the envelope to build up. When the conditions of temperature and pressure rise above a certain level, the pyrotechnic charge detonates causing serious damage.
So as to avoid such hazards, it is known to provide means to ensure the opening of the envelope when the temperature rises above a certain level. In fact, the opening of the envelope prevents the build-up of pressure inside it, and the pyrotechnic charge may thereby burn without detonating.
Patents FR2628833 and FR2652644 therefore propose to close the envelope by means of a base whereby the base is made integral with the envelope by means of an eutectic material.
When the temperature rises above a certain level, the eutectic material melts and unlocks the base. The latter is then pushed some distance away from the envelope by means of springs.
Such a device presents certain disadvantages. Where the means of deconfinement are specific to a given munition, they occupy a certain amount of space inside the envelope and may not be removed or replaced without a complicated intervention on the whole of the munition.
It is therefore necessary to design these means during the study phase of the munition and they may not be used to protect older munitions which have not been provided with such devices.
Moreover, as a general rule the eutectic material does not possess all the mechanical characteristics required to ensure a reliable bond between the two elements of the munition during all stages of its operation.
Patent FR2564965 proposes a deconfinement device which is totally external to the munition and which is temporarily fastened onto the latter by means of bands (for example during the different storage phases).
This device comprises a flexible linear shaped charge which is initiated by means of an igniting device comprising a firing pin and a primer. The firing pin is kept away from the primer by a lock in eutectic material.
A rise in temperature causes the eutectic material to melt thereby releasing the firing pin which initiates the primer thereby operating the flexible linear shaped charge.
Such a device also presents certain disadvantages.
For the firing pin to be able to initiate the primer, all the eutectic material must be evacuated from the firing pin housing. However, this material may only be evacuated via a few radial holes which risk becoming blocked during long periods of storage and which are no doubt not sufficient to ensure that all the material is properly evacuated.
The reliability of this device is therefore uncertain.
Moreover, if a deconfinement device, which is not installed on a munition, is subjected to a rise in temperature initiation would still take place at the risk of damage.
This device therefore also provides an insufficient level of safety.
Finally, it must be noted that the eutectic material is placed inside a case and that this case contains a thermal capacity which is likely to disturb the device, notably by modifying the temperature limits for sure functioning.